I don't think Faststone supports the IPTC format -- or at least it didn't 6 months ago and browsing their site, I still don't see any referance. To me that was the major deciding factor to go with XnView.
I used to use an older version of ACDSee. With it, I spent a little over a year scanning and cataloging thousands of pictures (Mom and Dad's pictures they had thrown in the closet or where ever). What I didn't understand was that version of ACDSee kept all those descriptions that I entered from the back of the photos in a seperate database. My computer crashed (virus in boot sector) and I ended up reformating the hard drive -- all the descriptions gone. I know I could have done better if I had understood the ACDSee application, but it has simplified things for me to go with applications that embed descriptions into the photo files (IPTC format) as opposed to keeping it seperate.
Now when I give my sister pictures, the descriptions go with the pictures through the IPTC header information in the photo files. The IPTC information is realy great way to sort and catalog the pictures. Pierre has provided good tools for working with that information -- thanks
In addition to the IPTC, XnView has been an intiutive application for me. I actually understand most of the stuff on the menus.